Algae create glue to repair cell damage

The reproductive secret of an environmentally damaging alga has been rumbled.

When strands of Caulerpa taxifolia break off to form separate organisms, the parent heals itself with a fast-acting natural glue. This helps the algae to spread rapidly, but might also prove an Achilles heel, aiding the ecologists fighting to banish it from the Mediterranean Sea.

Each alga is a single, supersized cell up to several metres in length. The cell looks like a fern, with central stems leading to finer fronds. When a frond is chopped off, by a passing power boat, for example, this leaves two new organisms. But it also leaves an injury a few millimetres wide in the cell.

Georg Pohnert and his colleagues at the Max Planck Institute for Chemical Ecology in Jena, Germany, have found out how the algae survive this traumatic birth. Their healing glue works a little like commercial epoxy resins, in which two chemicals are mixed to make a reactive adhesive that binds and sets very quickly.

When C. taxifolia is wounded, a chemical inside the cell called caulerpenin is broken down by an enzyme to produce a highly reactive molecule called oxytoxin 2. This immediately binds together proteins and their components, forming a gummy gel inside the cell that can plug the reproductive rent in just 30 seconds. Within an hour, the plug hardens into protective scar tissue.

"I don't know of any other wound-healing mechanism like this for a single-celled organism," says Pohnert, whose study appears in the journal Angewandte Chemie1.

Sticking place

Oxytoxin 2 itself is so reactive that the algae cannot keep a store of it, says Pohnert. "It's not stable enough and it's just too aggressive against proteins," he says, explaining why a fresh batch is made every time the algae need it.

But why doesn't C. taxifolia's healing process run rampant throughout the cell, turning its insides to jelly? "We'd love to know why the reaction is localized around the wound," says Pohnert. "At the moment, we don't know where the reaction starts or why it stops."

Algae are mostly water, but caulerpenin makes up about 10% of the rest of C. taxifolia's mass. Although not particularly toxic, the chemical seems to deter creatures such as sea urchins from eating the fronds. Still, Pohnert says that, until now, the algae's high concentrations of the chemical had been a mystery.

Great quell

The discovery could prove useful in combating a strain of the algae that invaded the Mediterranean in 1984 and has been an environmental headache ever since2. It smothers sea grasses, changing the local habitat and depriving fish of food. A similar plague off the California coast was tackled with aggressive chemical treatments, but these often kill all life in the area.

"Around Italy and France it is spreading a lot," says Enrique Segarra, who studies invasive species and is based at the Centre for Advanced Studies in Blanes, Spain. He says that nothing is being done to tackle the problem in much of the Mediterranean.

Pohnert has found that the chemical lysine can mop up all the caulerpenin, preventing Caulerpa's wounds from healing. "But to actually supply lysine in the natural habitat would be really tricky," he admits.